The present invention generally relates to firearms, and more particularly to barrel retaining mechanisms for semi-automatic and automatic firearms.
Various arrangements are known to secure the barrel of a firearm to the receiver or frame. One known basic barrel retaining system used is to form a simple threaded connection between the breech end of the barrel and the receiver or frame. Other arrangements have been employed, however, on semi-automatic/automatic auto-loading rifles like the military and law enforcement versions of the M4-type and M16-type carbines, and semi-automatic counterparts such as AR-15 type carbines. The extreme operating conditions of rapid-fire automatic weapons results in rapid wearing down of rifling in the bore of the barrel, thereby requiring periodic replacement of the barrel sometimes during the exigencies of combat. In addition, it is sometimes be desirable to swap out barrel configurations and/or lengths depending on changing field conditions or combat environments encountered in which the automatic carbines will be used. For example, shorter lighter barrels are often desirable for close-quarters engagement like building sweeps. Longer heavier barrels may be needed in other situations for improved accuracy when firing at greater distances. Accordingly, it is desirable that today's semi-automatic/automatic rifles have readily replaceable barrels and be quickly adaptable to the situation at hand.
A known barrel retaining system used in M16-type carbines provides a detachable barrel that may be separated from the upper receiver for replacement. One such arrangement is generally shown in U.S. Pat. No. 6,971,202. This arrangement utilizes a threaded nipple on the front of the receiver that receives a threaded cast aluminum or steel barrel nut having complementary mating internal threads. Except for the threading and sometimes castellated collar for gripping with a wrench, the barrel nut is a generally plain tubular structure and acts much as an ordinary nut. The breech end of the steel barrel has a short stub-like tubular extension that is equipped with an annular flange spaced inwards from the end of the extension. The barrel extension may be an integral part of the barrel or may be a separate tubular component that is threaded onto the breech end of the barrel. The barrel extension further contains internal bolt-locking lugs with angled feed ramps for loading cartridges into the chamber formed in the breech end of the barrel. The bolt-locking lugs in the barrel extension engage bolt lugs formed on the forward end of a rotatable and axially reciprocating steel bolt slidably mounted in the receiver to provide a steel-to-steel lockup for withstanding the forces of combustion when the rifle is fired. The barrel is attached to the receiver by inserting the barrel extension through the threaded nipple into the receiver until the barrel extension flange is abutted against the receiver. The barrel nut is then slipped partially over the stub portion of the barrel and flange, and threaded onto the receiver nipple thereby trapping the barrel flange between an annular shoulder formed in the barrel nut and the receiver to secure the barrel. In an alternative reverse arrangement of this type barrel retaining system, the barrel nut may be externally threaded and the receiver contains a bore having mating internal threads as shown in U.S. Patent Application Publication No. US2007/0033851. In either of the foregoing arrangements, the barrel is held to the receiver by trapping the barrel flange against the receiver with the barrel nut.
The foregoing combination barrel nut/barrel flange retaining system does not lend itself to rapid barrel swapping and makes it cumbersome to exchange barrels under field conditions. The barrels of the foregoing rifles also become extremely hot during rapid fire automatic mode or semi-automatic mode and are difficult to handle directly with unprotected hands. The handguard, which typically surrounds such barrels typically must be at least partially disassembled in some designs often requiring additional tools to gain access to the barrel nut. Specialized tools such as barrel nut wrenches may also be required to unthread and subsequently reinstall the barrel nut with an appropriate torque preload. In summary, the barrel exchange process with the conventional barrel nut arrangement is cumbersome and time consuming, and not well suited for rapid barrel swapping particularly under combat conditions.
An improved barrel retaining system having quick-change characteristics is desirable.